Presently there has become a revitalized interest in the Stirling engine in an attempt to improve its efficiency, cost and size. A basic Stirling engine design for example involves a piston/cylinder arrangement wherein a piston is driven by the use of hot and cold working gas. The gas is compelled to move from a cold space to a hot space continually and when the gas is hot it expands and pushes the piston in a first direction and when it is cold it is compressed by the piston moving back in the opposite direction to its original position.
Generally, the piston may be connected to a piston rod which in turn connects to a crosshead. This crosshead may then be coupled to a crankshaft which is to be rotationally displaced by the reciprocating movement of the piston. An improvement on this basic concept for converting between rotary and the reciprocating motion of the piston is disclosed in commonly assigned U.S. patent application Ser. No. 246,664 entitled Variable Stroke Swash Plate filed Mar. 23, 1981 for example.
However, a basic feature of the piston/rod relationship is to provide a sealing off of the chamber from the crosshead during operation of the engine. This becomes especially important due to the high pressures (approximately 1500 psi) involved in the cylinder and the use of hydrogen as a working gas.
There presently exists a piston rod seal which isolates the cylinder chamber from the crosshead during operation of the engine which is manufactured by Kommanditbolage United Stirling AB and Company (Sweden). This piston rod seal is depicted in FIG. 1 (labelled "prior art") wherein a piston 10 is shown disposed in a cylinder 12 and coupled to a piston rod 14 which in turn connects to a crosshead 16. A piston seal 18 is provided between the crosshead and the piston and is disposed about the piston rod. A compartment 20 is defined between the seal and piston containing hydrogen at a fluctuating pressure which varies during operation of the engine but is generally above 1500 psi. A rubbing seal 22 is provided which separates compartment 20 from another compartment 24 which is pressurized at approximately the minimum pressure in the system (1500 psi). Another rubbing seal 26 is provided separating compartment 24 from the crankcase 28 containing oil or other lubricant therein, with a scraper 30 preventing a build up of oil on the piston rod. Seal 26 and scraper 30 are spring loaded against the piston rod to enable their effective use.
A problem with the aforenoted arrangement is that the hydrogen-to-oil seal 26 which is continually spring loaded against the piston rod wears and the resulting deterioration causes a contamination of the hydrogen by the oil. This adversely affects the operation of the engine, shortens its usuable life period and require relatively frequent replacement resulting in expense and down time for the engine. There exists a need for a piston rod seal which provides for effective sealing while eliminating the wearing problems heretofore realized.